March 2005 doc.: IEEE 802.11-05/0105r3

IEEE P802.11Wireless LANs

DS Clarifications

Date: 2005-02-08

Author(s):Name Company Address Phone email

Mike Moreton STMicroelectronics mm2004@mailsnare.

net

Submission page 1 Mike Moreton, STMicroelectronics

AbstractThis submission provides draft changes to 802.11ma draft 0.5 to improve the description of the DS, Integration function service and Portal etc.

It also contains redefinitions of certain related terms (such as BSS) where the definition appeared to be incorrect.

It does not (it is believed) change any of the architectural concepts – just clarifies what already exists.

Finally it also specifies the service interface to the DS, as a genuinely implementation-neutral DS is aided by having a specified service interface.

Note that in many cases the justification for the change has been provided as a Microsoft Word Comment attached to the change. It is recommended that this document be viewed in a manner where comments are visible.

Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11.

Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>.

March 2005 doc.: IEEE 802.11-05/0105r3

DescriptionThis section contains justifications for some of the changes made to definitions in the proposed text that follows.

Change to name of Distribution ServiceIt is extremely confusing to have a Distribution Service and a Distribution System Service that are different things. Even the standard seems confused…

The former has been renamed the “MSDU Relay Service”

Also the use of DSS was somewhat confused between whether it was singular or plural. I’ve gone with the singular (as an abbreviation that is plural looks a bit strange).

Clarification of ESSThe current standard is confused as to whether integrated LAN devices are part of the ESS or not. The definition of ESS says “yes”, some of the diagrams say “no”. I’ve tried to make this consistent. I’ve said that they are part of the ESS, as a STA is unable to tell whether a remote STA across the DS is an 802.11 STA or not, so the distinction would be of no practical use.

Uncontrolled Port Frames to AP Do Not Transit the DSIf we have the concept that association allows the STA to access the DS, then the obvious extension for 802.11i is to say that association plus controlled port authorisation allows access to the DS. This is actually important as connection to the DS is conceptually meant to update the DS with the new STA location, so to avoid a DOS attack this should not happen until the controlled port is authorised.

However, the delivery of uncontrolled port frames to the AP must be possible before access to the DS is enabled. So clearly they can’t be going via the DS.

In principle, uncontrolled port frames should have been specified as being sent with fromDS and toDS false (which would give them the correct address format for their use) but it’s too late to change that. Might have solved a few other problems at the same time…

Addition of “Virtual MAC Entities”To the 802.1D Relay Entity each 802.11i MAC entity looks like a collection of virtual MAC entities – one per associated STA, and one for broadcast/multicast transmissions.

Changes to BSA and ESAThese were both defined in terms of a “conceptual area” whatever that means. I’ve changed them to “geographical area”.

Addition of MSDU Relay Service PrimitivesOne of the problems with the 1999 standard is that it didn’t define the service interface between the DS and the MAC. Leaving the DS unspecified doesn’t mean you shouldn’t define the interface to it – in many ways it’s even more important to do so. I’ve added a section that does this.

Submission page 2 Mike Moreton, STMicroelectronics

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Definition of WDSThere was no definition of WDS, so I’ve added one. Unfortunately the definition isn’t very good, because when you think about it the whole idea of a “Wireless Distribution System” breaks the DS concept. It should really be called a “Wireless Distribution System Medium”. Is that too big a change?

Submission page 3 Mike Moreton, STMicroelectronics

March 2005 doc.: IEEE 802.11-05/0105r3

Proposed Changes to the DraftAdd the following to the list of normative references in clause 2:

IEEE Std 802.1D™-2004, Standard for Local and Metropolitan Area Networks: Media Access Control (MAC) Bridges

ISO/IEC Technical Report 11802-5:1997(E), Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Technical reports and guidelines—Part 5:Media Access Control (MAC) Bridging of Ethernet V2.0 in Local Area Networks

Make the following changes:

3.2 access point (AP): Any entity that has station functionality and provides access to the distribution services system service, via the wireless medium (WM) for associated stations.

3.5 association: The service used to establish access point/station (AP/STA) mapping and enable STA invocation of the distribution system services (DSSs). MSDU Relay Service.

3.13 basic service area (BSA): The conceptual geographical area within which containing the members of a basic service set (BSS) may communicate. It may contain members of other Basic Service Sets.

3.14 basic service set (BSS): A set of stations controlled by a single coordination function. A set of stations that have executed the synchronization procedure described in clause 11.1. Note that membership of a BSS does not imply that wireless communication with all other members of the BSS is possible.

3.31 distribution MSDU Relay: The service that, by using association information, delivers medium access control (MAC) service data units (MSDUs) within via the distribution system (DS).

3.34 distribution system service (DSS): The set of services provided by the distribution system (DS) that enable enables the medium access control (MAC) to transport relaying of MAC service data units (MSDUs) between stations that are not in direct communication with each other over a single instance of the wireless medium (WM). These services include transport of MSDUs between the access points (APs) of basic service sets (BSSs) within an extended service set (ESS), transport of MSDUs between portals and BSSs within an ESS, and transport of MSDUs between stations in the same BSS in cases where the MSDU has a multicast or broadcast destination address or where the destination is an individual address, but the station sending the MSDU chooses to involve DSS. DSSs are provided between pairs of IEEE 802.11 MACs.

3.43 extended service area (ESA): The conceptual geographical area within which members of an extended service set (ESS) may communicate. An ESA is larger than or equal to a basic service area (BSA) and may involve several basic service sets (BSSs) in overlapping, disjointed, or both configurations.

3.55 infrastructure BSS: The infrastructure includes the distribution system medium (DSM), access point (AP), and portal entities. It is also the logical location of distribution and integration service functions of an extended service set (ESS). An infrastructure contains one or more APs

Submission page 4 Mike Moreton, STMicroelectronics

March 2005 doc.: IEEE 802.11-05/0105r3

and zero or more portals in addition to the distribution system (DS). An Infrastructure BSS is a BSS that contains one (and only one) Access Point.

3.56 integration: The service that enables delivery of medium access control (MAC) service data units (MSDUs) between the distribution system (DS) and a an existing, non-IEEE 802.11 local area network (LAN) (via a portal).

3.68 minimally conformant network: An IEEE 802.11 network in which two stations in a single basic service area (BSA) are conformant with IEEE Std 802.11, 1999 Edition.

3.83 portal: The logical point at which the integration service is provided. medium access control (MAC) service data units (MSDUs) from a non-IEEE 802.11 local area network (LAN) enter the distribution system (DS) of an extended service set (ESS).

3.123 Wireless Distribution System (WDS): A distribution system medium (or part of one) where the MAC used to access the medium is the MAC specified in this standard. This standard describes a frame format for use in the WDS, but does not describe how such a link would be established, how transmissions would be protected, or the filtering rules for broadcast/multicast transmissions.

5.1.1.4 Interaction with other IEEE 802 layersIEEE 802.11 is required to appear to higher layers [logical link control (LLC)] as a current style IEEE 802 LAN. This requires that the IEEE 802.11 network handle station mobility within the MAC sublayer. To meet reliability assumptions (that LLC makes about lower layers), it is necessary for IEEE 802.11 to incorporate functionality that is untraditional for MAC sublayers.

5.2 Components of the IEEE 802.11 architectureThe IEEE 802.11 architecture consists of several components that interact to provide a wireless LAN that supports station mobility transparently to upper layers.

The basic service set (BSS) is the basic building block of an IEEE 802.11 LAN. Figure 1 shows two BSSs, each of which has two stations that are members of the BSS.

It is useful to think of the ovals used to depict a BSS as the coverage area within which the member stations of the BSS may remain in communication. (The concept of area, while not precise, is often good enough.) This area is called the Basic Service Area (BSA). If a station moves out of its BSS BSA, it can no longer directly communicate with other members of the BSS.

Change the number of clause 5.2.1.1 to be 5.2.2, and renumber following clauses as appropriate. Make the following changes to the new 5.2.2:

5.2.1.1 2STA membership of a to BSS association is dynamicThe association between a STA and a A STA’s membership of a BSS is dynamic (STAs turn on, turn off, come within range, and go out of range). To become a member of a BSS, a STA joins the BSS using the synchronisation procedure described in clause 11.1.3.4 of this standard.

To become a member access all the services of an infrastructure BSS, a station shall become “associated.” These associations are dynamic and involve the use of the distribution system service (DSS), which is described in 5.3.2.

Submission page 5 Mike Moreton, STMicroelectronics

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Make the following changes to the old clause 5.2.2 and following clauses:

5.2.2 Distribution system (DS) conceptsPHY limitations determine the direct station-to-station distance that may be supported. For some networks this distance is sufficient; for other networks, increased coverage is required.

Instead of existing independently, a BSS may also form a component of an extended form of network that is built with multiple BSSs. The architectural component used to interconnect BSSs is the DS.

IEEE 802.11 logically separates the WM from the distribution system medium (DSM). Each logical medium is used for different purposes, by a different component of the architecture. The IEEE 802.11 definitions neither preclude, nor demand, that the multiple media be either the same or different.

Recognizing that the multiple media are logically different is key to understanding the flexibility of the architecture. The IEEE 802.11 LAN architecture is specified independently of the physical characteristics of any specific DS implementation. IEEE 802.11 does not constrain the DSM to be either data link or network layer based. Nor does IEEE 802.11 constrain a DS to be either centralized or distributed in nature.

The DS enables mobile device support by providing the logical services necessary to handle address to destination mapping and seamless integration of multiple BSSs.

An access point (AP) is a STA that provides access to the DS by providing DS services the DSS in addition to acting as a STA.

Figure 2 adds the DS, DSM and AP components to the IEEE 802.11 architecture picture.

Submission page 6 Mike Moreton, STMicroelectronics

March 2005 doc.: IEEE 802.11-05/0105r3

Figure 2—DSsDS, DSM and APs

Data move between a BSS and the DS via an AP. Note that all APs are also STAs; thus they are addressable entities. The addresses used by an AP for communication on the WM and on the DSM are not necessarily the same.

Data sent to the AP’s STA address by one of the STAs associated with it, conceptually transits the DS, unless it is an uncontrolled port frame in an RSNA, in which case it will be formatted as if it is to be sent to the DS, but does not in fact transit the DS.

One possible implementation of a DS is an IEEE 802.1D bridged LAN. Such a possible implementation is described in clause XXX, but other implementations of the DS are specifically not excluded.

A Wireless Distribution System (WDS) is a DSM (or part of one) where the MAC in use within the DSM is that defined in this standard. This standard defines a suitable frame format for use in the WDS, but does not specify the method of establishing such a connection.

Update the diagram in 5.2.2.1 “Extended service set (ESS): The large coverage network” as follows:

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March 2005 doc.: IEEE 802.11-05/0105r3

5.2.4 Integration with wired LANs

To integrate the IEEE 802.11 architecture with a traditional wired LAN, a final logical architectural component is introduced—a portal.

A portal is the logical point at which MSDUs from an integrated non-IEEE 802.11 LAN enter the IEEE 802.11 DS. For example, a portal is shown in Figure 6 connecting to a wired IEEE 802 LAN

Submission page 8 Mike Moreton, STMicroelectronics

March 2005 doc.: IEEE 802.11-05/0105r3

Figure 6—Connecting to other IEEE 802 LANs (Unchanged)

.All data from non-IEEE 802.11 LANs enter the IEEE 802.11 architecture via a portal. The portal provides logical integration the Integration Function Service between the IEEE 802.11 architecture DS M and existing wired other LANs. The Integration function service is responsible for any addressing or frame format changes that might be required when frames pass between the DS and the integrated LAN, and terminating any protocols that might be required to maintain the STA to AP location mapping.

It is possible for one device to offer both the functions of an AP and a portal; this could be the case when a DS is implemented from IEEE 802 LAN components.

In IEEE 802.11, the ESS architecture (APs and the DS) provides traffic segmentation and range extension. Logical connections between IEEE 802.11 and other LANs are via the portal. Portals connect between the DSM and the LAN medium that is to be integrated.

Make the following changes to clause 5.3 “Logical Service Interfaces”

5.3 Logical service interfaces

The IEEE 802.11 architecture allows for the possibility that the DS may not be identical to an existing wired LAN. A DS may be created from many different technologies including current IEEE 802 wired LANs. IEEE 802.11 does not constrain the DS to be either data link or network layer based. Nor does IEEE 802.11 constrain a DS to be either centralized or distributed in nature.

Submission page 9 Mike Moreton, STMicroelectronics

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IEEE 802.11 explicitly does not specify the details of DS implementations. Instead, IEEE 802.11 specifies services. The services are associated with different components of the architecture. There are two categories of IEEE 802.11 service—the station service (SS) and the Distribution System Service ( DSS). Both categories of service are used by the IEEE 802.11 MAC sublayer.

The complete set of IEEE 802.11 architectural services are as follows:

a) Authenticationb) Associationc) Deauthenticationd) Disassociatione) Distribution MSDU Relayf) Integrationg) Confidentialityh) Reassociationi) MSDU deliveryj) DFSk) TPC

This set of services is divided into two groups: those that are part of every STA – the Station Services (SS), and those that are part of a provided by the DS – the Distribution System Service(DSS).

Make the following changes to clause 5.3.2 “DSS”

5.3.2 DSSThe service provided by the DS is known as the DSS.

These services are This service is represented in the IEEE 802.11 architecture by arrows within the APs, indicating that the services are service is used to cross media and possibly address space logical boundaries. This is the convenient place to show the services in the picture. The physical embodiment of various services may or may not be within a physical AP.

An AP is a logical entity and the functions described may be shared by one or more physical entities.

The DSSs are DSS is provided by the DS. They are It is accessed via an AP which is a STA that also provides DSSs access to the DSS. A STA that is providing access to DSS is an AP.

The DSSs services that comprise the DSS are as follows:a) Associationb) Disassociationc) Distribution MSDU Relayd) Integratione) Reassociation

DSSs are specified for use by MAC sublayer entities.

Figure 7 combines the components from previous figures with both types of services to show the complete IEEE 802.11 architecture.

Submission page 10 Mike Moreton, STMicroelectronics

March 2005 doc.: IEEE 802.11-05/0105r3

Figure 7—Complete IEEE 802.11 architecture

5.3.3 Multiple logical address spacesJust as the IEEE 802.11 architecture allows for the possibility that the WM, DSM, and an integrated wired LAN may all be different physical media, it also allows for the possibility that each of these components may be operating within different address spaces. IEEE 802.11 only uses and specifies the use of the WM address space.

Each IEEE 802.11 PHY operates in a single medium—the WM. The IEEE 802.11 MAC operates in a single address space. MAC addresses are used on the WM in the IEEE 802.11 architecture. Therefore, it is unnecessary for the standard to explicitly specify that its addresses are “WM addresses.” This is assumed throughout this standard.

Submission page 11 Mike Moreton, STMicroelectronics

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IEEE 802.11 has chosen to use the IEEE 802 48-bit address space (see 7.1.3.3.1). Thus IEEE 802.11 addresses are compatible with the address space used by the IEEE 802 LAN family.

The IEEE 802.11 choice of address space implies that for many instantiations of the IEEE 802.11 architecture, the wired LAN MAC address space and the IEEE 802.11 MAC address space may be the same. In those situations where a DS DSM that uses MAC level IEEE 802 addressing is appropriate, all three of the logical address spaces used within a system could be identical. While this is a common case, it is not the only combination allowed by the architecture. The IEEE 802.11 architecture allows for all three logical address spaces to be distinct.

A multiple address space example is one in which the DS DSM implementation uses network layer addressing. In this case, the WM address space and the DS DSM address space would be different.

Note that IEEE 802.11 STAs within a single ESS share the same address space, as this is required by the reachability requirement from the definition of an ESS. The DSS uses this same address space, even where the DSM uses a different address space.

The ability of the architecture to handle multiple logical media and address spaces is key to the ability of IEEE 802.11 to be independent of the DS implementation and to interface cleanly with network layer mobility approaches. The implementation of the DS is unspecified and is beyond the scope of this standard.

Make the following change to the first two paragraphs of clause 5.4:

5.4 Overview of the servicesThere are several services specified by IEEE 802.11. Six of the services are used to support MSDU delivery between STAs. Three of the services are used to control IEEE 802.11 LAN access and confidentiality. Two of the services are used to provide spectrum management.

This subclause presents the services, an overview of how each service is used, and a description of how each service relates to other services and the IEEE 802.11 architecture. The services are presented in an order designed to help build an understanding of the operation of an IEEE 802.11 ESS network. As a result, the SSs and DSSs services that are part of the SS and DSS are intermixed in order (rather than being grouped by category)

Make the following changes to clause 5.4.1.1:

5.4.1.1 Distribution MSDU RelayThis is the primary service used by IEEE 802.11 STAs. It is conceptually invoked by every data message to or from an IEEE 802.11 STA operating in an ESS (when the frame is sent via the DS). Distribution is via a MSDU Relay is part of the DSS.

Refer to the ESS network in Figure 7 and consider a data message being sent from STA 1 to STA 4. The message is sent from STA 1 and received by STA 2 (the “input” AP). The AP gives the message to the distribution MSDU Relay Service of the DS. It is the job of the

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distribution MSDU Relay Service to deliver the message within the DS in such a way that it arrives at the appropriate DS destination for the intended recipient. In this example, the message is distributed to STA 3 (the “output” AP) and STA 3 accesses the WM to send the message to STA 4 (the intended destination).

How the message is distributed within the DS is not specified by IEEE 802.11. All IEEE 802.11 is required to do is to provide the DS with enough information for the DS to be able to determine the “output” point that corresponds to the desired recipient. The necessary information is provided to the DS by the three association related services (association, reassociation, and disassociation).

The previous example was a case in which the AP that invoked the distribution MSDU Relay Service was different from the AP that received the distributed relayed message. If the message had been intended for a station that was a member of the same BSS as the sending station, then the “input” and “output” APs for the message would have been the same.

In either example both examples, the distribution MSDU Relay Service was logically invoked. Whether , whether the message actually had to traverse the physical DSM or not is a DS implementation matter and is not specified by this standard.

While IEEE 802.11 does not specify DS implementations, it does recognize and support the use of the WM as the DSM. This is specifically supported by the IEEE 802.11 frame formats. (Refer to Clause 7 for details.)

Delete clause 5.4.1.2 “Integration”

Make the following changes:

5.4.2 Services that support the distribution serviceThe primary purpose of a MAC sublayer is to transfer MSDUs between MAC sublayer entities. The information required for the distribution MSDU Relay Service to operate is provided by the association services. Before a data message can be handled by the distribution MSDU Relay Service, a STA shall be “associated.”

To understand the concept of association, it is necessary first to understand the concept of mobility.

5.4.2.2 AssociationAssociation is the service by which a STA that is a member of a BSS gains access to the DS, and in particular the MSDU Relay Service of the DS. Use of this service is also an explicit request to the AP to inform the DS of the location of the STA so that MSDUs can be delivered to it. Association is part of the DSS.

The Association service is used when the STA has performed an ESS-transition, or when it has no information about previous associations.

In a pre-RSNA, the association service is invoked by the exchange of Association frames (see clause 7).

In an RSNA, there are additional steps.

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The exchange of Association frames invokes the creation of a new Pairwise Virtual MAC Entity, and its associated IEEE 802.1X Authenticator PAE for the association. The STA is not granted access to the DS, but may send frames to the AP’s IEEE 802.1X Uncontrolled Port as such frames do not transit the DS (even though they are formatted as if they do).

The two parties to the association then carry out the selected AKM (see clause 8) using frames sent to each other’s IEEE 802.1X Uncontrolled Port. On successful completion of the AKM, the IEEE 802.1X Controlled port is authorised, and access to the DS is granted.

To deliver a message within a DS, the distribution service needs to know which AP to access for the given IEEE 802.11 STA. This information is provided to the DS by the concept of association. Association is necessary, but not sufficient, to support BSS-transition mobility. Association is sufficient to support no-transition mobility. Association is a DSS.

Before a STA is allowed to send a data message via an AP, it shall first become associated with the AP. The act of becoming associated invokes the association service, which provides the STA to AP mapping to the DS. The DS uses this information to accomplish its message distribution service. How the information provided by the association service is stored and managed within the DS is not specified by this standard.

Within a robust security network (RSN), this is different. In an RSNA, the IEEE 802.1X Port determines when to allow data traffic across an IEEE 802.11 link. A single IEEE 802.1X Port maps to one association, and each association maps to an IEEE 802.1X Port. An IEEE 802.1X Port consists of an IEEE 802.1X Controlled Port and an IEEE 802.1X Uncontrolled Port. The IEEE 802.1X Controlled Port is blocked from passing general data traffic between two STAs until an IEEE 802.1X authentication procedure completes successfully over the IEEE 802.1X Uncontrolled Port. Once the AKM completes successfully, data protection is enabled to prevent unauthorized access, and the IEEE 802.1X Controlled Port unblocks to allow protected data traffic. IEEE 802.1X Supplicants and Authenticators exchange protocol information via the IEEE 802.1X Uncontrolled Port. It is expected that most other non-AKM protocol exchanges will make use of the IEEE 802.1X Controlled Ports. However, a given protocol may need to bypass the authorization function and make use of the IEEE 802.1X Uncontrolled Port.NOTE—See IEEE P802.1X-REV for a discussion of Controlled Port and Uncontrolled Port.13

At any given instant, a STA may be associated with no more than one AP. This ensures that the DS may determine a unique answer to the question, “Which AP is serving STA X?” Once an association is completed, a STA may make full use of a DS (via the AP) to communicate. Association is always initiated by the mobile STA, not the AP.

An AP may be associated with many STAs at one time.

A STA learns what APs are present and then invokes the association service requests to establish an association by invoking the association service. For details of how a station learns about what APs are present, see 11.1.3.

Make the following change to the description of Class 3 frames in clause 5.5:

c) Class 3 frames (if and only if associated; allowed only from within State 3):1) Data frames

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— Data subtypes: Data frames allowed. That is, either the “To DS” or “From DS” FC bits may be set to true to utilize DSSs the DSS.

Change figure 9 in clause 5.6 and the immediately following paragraph as follows:

Figure 9—IEEE 802.11 architecture (again)

An IBSS consists of STAs that are directly connected. Thus there is (by definition) only one BSS. Further, because there is no physical DS, there cannot be a portal, an integrated wired LAN, or the DSSs DSS. The logical picture reduces to Figure 10.

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Add the following new clause after the existing clause 6.1.3 “MSDU ordering” and renumber as appropriate.

6.1.4 MSDU formatThis standard is part of the IEEE802 family of LAN standards, and as such all MSDUs are LLC PDUs as defined in ISO/IEC 8802-2: 1998. In order to achieve interoperability, implementers are recommended to apply the procedures described in ISO/IEC TR 11802-5: 1997(E) (previously known as IEEE 802.1H) with specific attention to the operations required when passing MSDUs to or from LANs or operating system components that use the Ethernet frame format. Note that such translations may be required in a STA whether it is an AP or not.

Submission page 16 Mike Moreton, STMicroelectronics